Btrfs: remove no longer used logged range variables when logging extents

The logged_start and logged_end variables, at btrfs_log_changed_extents,
were added in commit 8c6c592831a0 ("btrfs: log csums for all modified
extents"). However since the recent simplification for fsync, which makes
us wait for all ordered extents to complete before logging extents, we
no longer need those variables. Commit a2120a473a80 ("btrfs: clean up the
left over logged_list usage") forgot to remove them.

Reviewed-by: Nikolay Borisov <[e-mail]>
Signed-off-by: Filipe Manana <[e-mail]>
Signed-off-by: David Sterba <[e-mail]>

fs/btrfs/tree-log.c

···
 	struct extent_map *em, *n;
 	struct list_head extents;
 	struct extent_map_tree *tree = &inode->extent_tree;
-	u64 logged_start, logged_end;
 	u64 test_gen;
 	int ret = 0;
 	int num = 0;
···
 
 	write_lock(&tree->lock);
 	test_gen = root->fs_info->last_trans_committed;
-	logged_start = start;
-	logged_end = end;
 
 	list_for_each_entry_safe(em, n, &tree->modified_extents, list) {
 		/*
···
 		if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags) &&
 		    em->start >= i_size_read(&inode->vfs_inode))
 			continue;
-
-		if (em->start < logged_start)
-			logged_start = em->start;
-		if ((em->start + em->len - 1) > logged_end)
-			logged_end = em->start + em->len - 1;
 
 		/* Need a ref to keep it from getting evicted from cache */
 		refcount_inc(&em->refs);